She said she supported it while it was being negotiated, and later (as a candidate, when the final text was available) said she opposed the final form, and that it no longer had the specific features she expected the final form would have when she supported it.
The timing of this is peculiar, but if it has nothing to do with HRC, we'll simply have to wait and see if that is the case.
If it had to do with HRC, they could wait; if anything connected to the election, it has to do with their actual support for TPP and concern that no successor to Obama will approve it, so their best chance is for it to get passed and signed this year (given the statements already made by Republican leaders that that isn't going to happen before the general election, probably in the lame duck session after the election.)
But they won't, because they're doubling down.